Telephone-exchange automatic trunking system.



A I T. e. MARTIN. TELEPHONE EXCHANGE AUTOMATIC TRUNKING SYSTEM.

` 4 APPucATmN FILED MAR. 1. 1910,

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- Patented Aug. 21, l917.

. 4sHE`ETs4sHEIT`1 v 'l mi \O T. s. MARTIN. i TELEPHONE` EXCHANGE AUTMATIC TRUNKING SYSTEM.

APPLICATION FILED MAR. I. 1910. A' 1,238,039. Patented Aug. r,21, 1917.

l K LG. MARTi-M TELEPHONE. EXCHANGE AUTOMATIC TRUNKING SYSTEM.

APPLTCATION `FILED MAR. l. 1910.` 152158,039'

v mmmmwmd y www Patented Aug. 21, 1917.

T. G. MARTIN'.

TELEPHONE EXCHANGE Auwmmc IRUNKING SYSTEM.

APPLICATION FILED MAR. l. 1910.

SGR. m Q www@ k TALBOT e. MARTIN. or Grimace, rumors,

"mr AvAiLAai."

Assienon To `an'roxane-T10 'ELECTRIC CUM- 'Pmz orcHIcAGc. xLLAINoIs, A coaromrronor ILLINOIS.)

mELnrHoNE-EXCHA'N'GE To alla/:hom it concern.' l y l Be it knownffthatl, TALBOT. GLMARTIN,

.a citizen ofthe United. States 0f America,

and resident of Chicago, Cook county, Illi-- nois,l have invented a certain new and useful Improvement in Telephone-Exchange Auto matic '.Ilrunking Systems, of whichthe fol-A lowing is a specificatin- K My invention relates to automatic'or senuautomatic telephone exchange SysteIIls` in general, but more particular y/ to Vthose in lwhich provision. isfmadeffor enabling a sub- 4. scriber of one exchange to call a subscriber lof another exchange, which .exchanges are of dii'erent character. For example, automatic telephone vexchanges may be of the three=wire type-that is 'to say, 'of that char-- acte;- -injwhich an operatin V'ground ispro- \vided at thegsubstation o each telephone line, and in which the automatic switches at 'the exchange or central station' are respon# sive to Callingdevices which control the ground connections at the substations.', Again, systems of this kind' may be of the two-nire type-that is to say, ofthe kind in wvl-.ich no operating-.g`rounds a1-eeni- 'ployed at the substationsifof the telephone lines, and in which the automatic switches i lat the exchange' or central station Vare conline in series.

trolled. over tile two sides of' the telephone It some -tmes happens that a necessity arises for efficient service between a three-wire system and a two-wire system, and insuch case specialprovision must be made for' taking care cf'calls from one exchange to the other.

Generally stated, the object ofk my invention is the provision of improved means for trunkin'g between systems or exchanges of `different types, whereby a subscriber of one system may call a subscriber of the other system, and vice versa, with theI same, or substantially the same, facility and eiiiclen'cy y that a subscriber of either exchange would construction and arrangement W call another subscriber of the same exchange.

A special object is to provide an in'ipiovedA construction and arrangement whereby.i trunking may be .carried on from a threewire to a two-wire system, as-above defined;

Another object is vto provideV an improved ereby trunking may be effected from -a two-wire te three-wire system, as"abovc.defined. kwam' abject is the v orcvlsionof a lrei l lSpeelt-mation of Letters 15a1 :e1:ii 5. lApplication nled'lpicli 1, li. Serta'lNc. 546,581..

AUTOMATIC irnnnxmegsxsfrnm.

Patenteaaug 21, 1917.

peter fer-.usa ai. @rnking ,from a three wire to a twowire system, as-above defined,

which repeaterjis adapted toreceive the calling .impulses vtransmittedover' the .three-,i

wire; line circuit, and'i 'to then 'repeattind transmit the same; overthef twdyvire line circuit tothe othergv exchange.- l j l' l Another -objectis`-the iprovis1on oi a re-f '.peater foruse in, trunkingfrom a two-wireA which repeateris adapted-to receive the call-- ing impulses transmitted,overI the two-'Wire line circuit, and to then repeat and 'transf' circuit mit the same over the threefwireline :to the other exchange. A

Another object is to provlde animproved construction and arrangement wherebyacalling subscriber may signal the called subscriber by an additional movement of the'x' dial at the substation ofthe calling line.

It isalsoan object to provide certain details and' features of improvement and combinations tendingto increase the'- general exchange system of this particular character. To theforeging and other useful ends my invention consists in matters hereinafterset forth and claimed.

In `the accompanying drawings, which show a telephone system embodying. the principles of my invention, Figure 1 shows diagrannnatically automatic central oce vswitching apparatus of the usual type'. A

'efficiency and serviee -abilityof a telephone' represents a subscribers substation, While.

` at C the line switch allotted to the `line conductors of substation A is shown. The mas* ter switch D controls the line switches of the group of which the line switch `C is a .member E indicates a first selector switch and F represents one of my peeters.

Fig. 2 represents automatic'central office switching apparatus of antwo-wire system',

improved revi7..,-a*y system in'which va ground connection.

is not employed at the subscribers station for operating' switches. At N is lshown a first selector Switch, While at O a 'connector is represented. A. central cnice rin er gen# erator LA andbusy signaling machine M? are alsoshown. 'To the line conductors of substation A" thereA is allotted the 'line 'switch C- whichi switch D". Fig. 9

also repiesents automaticjcelitf 11.-

icc

ontrolled by the master oliice apparatus nof a two-.Wire system. H indicates a rst'selector switch, while at I is shown another of my improved repeaters for relaying impulses'to another exchange. ,Fig 4, shows additional central oiice 1 and 4 belongs to onerexehange, while the two-wire apparatus of Figs. 2 and 3 belongs to a secoridexchange.. For the purpose of furnishing current/for ,operating the switches y, and. for 'talking purposes a number of bat-l i teiiesB are,shoivn,feach havingone. termi# nal'grounded There may, however, `be but `IWone battery, or preferably, iffth'e exchanges- 'are some distance apart,-,one batteryfmay be provided foreach exchange oliicer' sog . Figs. 1 and 2 taken vlvtogether represent' diagrammatically the central office apparatus involved in establishing a connectioii.

fromjhe substation A to thesub'station-A.y

Fig.- 1 represents a connection exteiidedffrom substation A through a tliree-"wiree'xy .i v p "impulse spriiig-22- 'In `this operation' the change to a twoivire exchange -in Figi. 2,'

- .where-,the connectioniscompletedlwith the v. i f.

substation AH Figs. 3 and 4 represent paratus by means of which the substation A may obtain connection with the substation Af The apparatus shown in' Figs. 1 and 2 is is shown in its normal position.^'

central :office 1px lshown operated, while that of Figs.' 3 and l The substation A may belet any suitable" or approved type. The one in"connection f2 withwvhiclii'have elected to illustrate my invention comprises, 'among other details, a re` ceiver 2 and switch hook 3 for controlling the substation circuits, which controllingopdiumo any suitablemeans, such as the camarms 4, and '6.' As the switch hook is `erations are accomplished through the mef lowered `the cam-arm 4 monientarilv ressesI the release springs 7, Sfand 9 intoengage ment', 'whereby the substation line conductors may be grounded -When the switch-hook is down the cam-arm 5 maintains a contact between the springs 10 simultaneously.

and 11,` thereby bridging the ringer 12 in series with the condenser 13 'across the line. The vsubstation ground circuit is normally brokenbetween the ground springsl and l5. by thecamarm 6, but when said' springs are together. then ground potential is' provided from the battery to the ground post .16 and'to'the release spring 7, as usually the case inA telephones of this type'. The said lsprings 21 and one vi'j'ouiid impulse. l lng'as'the dialmis out o normal position the across the lineeonductors 309 and 310.

'the impulse wheel 311A returns tomornial posubstation comprises the usual transmitter 17, induction-coil 18. having the primary winding 19 and secondary winding 20. Being an automatic substation it is provided with the usual vertical and rotary impulse Said substation is, of course, provided with a dial (not shown) which is secured to the shaft 23, together with the locking dog 24. Furthermore,l there is a locking cam that locks the dog 24 while ,the receiver is on the switch hook to prevent rotation of the dial. For operating i the impulse springs 21 and 22 the substation is provided with an impulse whee12l5 that is securedto the shaft 23, which impulse wheel carries on .its periphery the so-called vertical impulse teeth 27, and one rotary impulse tooth 28. F urtherniore, the rotary impulse spring 22 is of such construction that, when ,the dial is turned forward for the first digit,

the rotary impulse toothV 2S momentarily presses the said impulse spring onto the ground post 16, whereby the rotary line con-.-

ductoiis given a preliminary impulse for 't'eeth engage the vertical limpulse spring 21,

and after'tliey; havecompletedtheir wor-k the rotary impulse tooth 'op'e'rates the rotary r`'sn'b`scrigb'ei"s vertical line conductor 29V is first v"given a "number of groundimpulses and then the rotary' line conductor '30 is` given It will'beV seen that as dog 2; perinits"th`e primaryeircuitl springs lrafnd"32 to ,sepa'ratc, thus preventing the iinpi'ilse's' that' are ,deliifjer'ed to either line condiiptdrlfrompassing to the other. Means `whereby subscriber may signal a called subscriber comprises. the' push-,buttonI 32 wiich, when pressed. carries the spring 3l out offengagenient with thecontact point 35 and intoengageinent'with the contact point 3h', whereby the vertical -linejcoiiductor 2!) The substation Af is of theisarne general type asthe substation A, butis modified T5014` and toengage. spring' 3Q2.` B v thisvac tiointhe circuit through the ringer 303 and' condenser`304is opened, and a'bridge consisting of theV transmitter 305,; receiver 306 and` impulse lsprings 307 and-.308 is closed As sition after the `dial has been rotated=to call fa number.. .the teeth 3,12 torce the limpulse eser AvAiLAeLE COP* sprin 308, thus' momentarily Iopening the bridge across the 'line a number of times, corresponding to the digit called. f

The line .switches C and C are similar `to the line Iswitches'disclosed. in British Patent No. 26,301 of 1906, Western Electrician i of- Chicago, Ill.,- .of Jan. 25,1908, and the America/w Telephone Journal of Chicago,l Ill., of June, V1908, the vswitch C being 1 0 modified slightly to operate in a two-wire system. The master switch D is similar in loperation and construction to the master j switch shown in the above publications.

i The master switch D is of the same gcn- .15 eral type as themaster switch D, b"utof a somewhat' dierentconstruction. In the master switch D several 'steps of the ratchet .El c 'i wheel 313 are required to rota'te the plunger shaft sutiicientlyto carry the idle plungers from one trunk to another. Rigidly secured, to the ratchetwheel 313thereis a notched.'

" wheel 314 composed preferably of insulating material. This notched wheel 314 controls a couple fof springs 315 and 316. The

notches inthe wheel 314 are so spaced 'that the springs 316and 315 may Vseparate only when the plungers that are in locking en* Agagement .with the plunger shaft are in a positiondirectly. in front of a-tru'nk terminal. `When a line switch operates Athe circuit of the motor magnet 319 is first closed by\the relay 317, which is energized through 'the wiper1318. As .soon as the ratchet wheel 3l3lis'rotated one step the springs 31'5 andl 316`are forced into engagement. The motor magnet" will' then continue to operate until ,\the `plu'ngers reach the next trunk, when the spring 315 drops into.y the nextnotch of the whehl 314, thus opening the circuitof the 40 mot r magnet 319, since in the meantime the circi it of relay 317 lasbeen broken by the wiper 318. The plunger shaft is so connected uifith the ratchetl wheel thata continued rotary motion of said wheel gives to the shaft a reciprocating motion to move the plungers yback'iand forth in front of the trunl'` tdrminals.' After' the plungers reach the limit of their travel in one direction they arribntloved successively past the trunks in the reverse direction.

"Phe selector switches E, N, H andJ are o the general type shown in United States llisttcis Patent#815,321, issued March 13, M1906, `to Keith, Erickson and Erickson. In this instance the usual bridge-cutoff relay and i` rmal conductors arecomitted. The select switches Hand N are modified and arranged to operate in connection fwith a twowire' system, while the switches E and J operate in conjunction with the usual sysf-"tem'employing a ground at the subscriberssubstation.

' The connector switch K is of the gfiieral typeiof connector switch shown in United States Letters Patent" 815,176LA issued March 13, 1906, vto Keith, Erickson and "Erickson, and is, as usual, connectedv to the ringer generator L and busy signaling ma- Jchine M. lThe connector O is- `or the same general type as theA connector K, being modi- Atied somewhat, however, to operate in a twov wire system. In the connector O the. operation of 'the ringer-.relay for bridging the terminals of the ringer generator across the called line-'is not contingent upon the callingI subscriber pressing a signaling button, but operates automaticallywhenthe side switch passes to third position. `After the called subscriber answers, however, the energizing circuit through the ringer relay is broken.

The repeater F is adapted to receive-imf' pulses' from a three-wire central office or substation, and to repeat these impulses to operate switches in a two-Wire exchange--` that is, the repeater F is the connecting link between a-'three-wire and a two-wire ex change, and comprisesthe usual vertical and rotary line relays 37 and 38 connected in series with the windings 39 and '40 of the4 differential relay 41. The rotary -magnet 42 is provided with anarmature-43 for rotating the ratchet wheel 44. Secured tothes'ame shaft with the ratchet wheel 44.are the wiper arms 46 and 47. The rotary magnet 42 isv so arrangedithat each time the dial reaches-'normal position'therotary magnet 42`energ1zes and the armature 43 moves the ratchet wheel 44 in its'- advanced position.

When the armature pawl 49 is attracted, thej ratchet wheel is then free to restorel to normal position. The frelay 50, upon energizing, attracts its armature 51 into contact with the contact point 52, thereby bridging vthe impedance coil 53 across the outgoingI trunk conductors.

Therepeater I (Fig. is adapted to receive impulses from a twowire substationl andto repeat these impulses to the switches of a three-wire, exchange `(Fig. 4). The re'- peater I, then, vis the connecting link beftween the two-wire exchange'and the threewire exchange in the same manner in which the repeater F 1s the collecting link between the .three-wireand ytwo-wire central offices.

The repeater I comprises-the usual doublewound line relay 54 comprising the windings and 56, which are bridged between the battery terminals andthe trunk conductors. 'llhe slow acting relay 57` controls lcertain "circuit connections, as-fwill be. explained.

The slow relay 58 controls the energizing circuitv of the quick andslow acting release relays 59 and 60. By slow acting is meant that, when the relay is energized and inanoperated position, the saidrplay will remain'. 1n its ,operated position'fora vshort timeA after the energizingcircuit i "'brokexn A 'clearer understandingg'o yi-'improved repeaters may be had from lana'tion' of their operation. `when the rotar Y impuis'e s rino' onto the @round .i ,n 1v

post 16, thereby closing airenergizing circuit extending from the substation ground G through the cooperating ground A'springs 11 and 15, ground post 1G, rotary impulse spring 22 to the rotary line conductor 30, bridge-cut-olf soi-ings 93 kand 63, trip magnet 01, through the motorvmagnet relay springs 01 and interrupterfsprings and 67, through'the winding otthefmotol" magnet-68 to the battery lead 69.- Thetrip magnet 01 hasta" comparatively high resist` ance and does not permit suilicient current to flow to operate the motormagnet 68'. As soon as the trip' magnet is energized fits armature isattracted and the plunger thrust ger enters -the bank terminal an energizingr circuit is elosedwtlnough the motor, magnet. relay 70-of thehiaster switch.. The motor magnet GS inturn energizes and operates to rotate the ratchetwheel 71, thereby vplacing the idlelplungers opposite-the nextidle bank terminal. The circuit through the relay 70 extends from` ground Gr2-th1jough the Windturc S1 engages the ratchet wheel i71'and i rotates. the latter one step. :VVhenthe armaster'switch'bank, th'roughfthe wiper 74 to the individual segment 75 `l`(which "corresponds to 'the trunk terminal just engaged),

conductor 76, line switch bank springs I77 and 78, through the winding ot' the release magnet 79' to the battery. lead 69,thence cuit on accounto'fthe comparatively high resistance of relay 70. .The motor li'nagnet, upon energizing. attracts-its"armatur 81, whereby the pawl u p ortthe end ofthe-.armamature S1 iis attracted'` against the magnet cores the interrupter springs .andv 67 disengage, thereby breaking the energizing 'cir-y cuit of the motor magnetGS. `'The cam arm operated to advance the plunger shaft V84 and, consequently, all idle plungers that may be in normal position one-step to' anotherA bank terminal. Also, the Vmaster switch bank wiper 74 is carried from the contact 75,Which corresponds to the trunk line engaged, to another contact correspondbetween ing to the bank terminal before which the idle plungers are now resting. At the instant that the plunger enters the bank terminal the following bank springs are pressed into contact: 85 and`86, 87 and 88, 89 an90, and 77 and`78. The engagement of the springs 87 and 88 establishes a positive guarding potential, which is transmitted by the private normal conductor 91 to the connectog private bank Contact corresponding to the line of substation A. This potential 'projects .the line to the calling subscriber from being called by another while the prof tect'ed line is in nse. Also, when the springsl S7 and 88 engage, an energizing circuit is establishelj rough the bridge-cutoii' relay 92 to t e ldittery lead 69 thence throng? battery B` to ground G. his relay, upon energizing, yoperates to break'the contactlv the springs 62,' 63 and 93 and to carry the spring- 93 into contact with the spring 94e. 'lhedisengaging of the springs trip magnet 01. The guarding potential at the master switchgbank' for protecting the 62, 63 and 93 disconnects the subscribers line conductors 29 and 30 from the line switch trunk ,line'conductors 95 an"d96`:'t'rom being i seized by another lineswtch extends from the l battery lead 69, through the release magnet 79 into an idle bank terminal. When the plun- -an'd bank springs 78 and 7 7 to the'individual the trunk' line,` conductor 95. manner the engagingof rthe bank springs S9 and, 90 extends the subscribers rotary line conductor 30 to the trunk line conductor 96. Y The trunk lineconductors 95 and' 96' terminatein .the first-selector switch E and, now, when the dial returnsjio normal position for the first digit, the vertical line relayis energized .a numberbf times `dependingupon the digit called. n The digit called being 2 thevertical impulse spring i 21 is pressed onto the ground post 16 twice, thereby closing an energizing circuit each time through the vertical line relay 97` ofy the first selector E. This circuit extends.

from the substation ground Gr through the ground post and' impulse spring 21 `to the vertical line conductor 29, banksprings 85 and S6, side switch wiper '98, vertical line relay 97 to the' battery lead 69, thence y through battery B to ground G.. Each time thatthe vertical line relay 97 encrgizes, theV springs 99 and 100 1are pressed 'into contact,

therebyA closing a 'circuit through the ver 82, being in engagement with4 ie pin 83, is

tical magnet 101 extending from ground battery B to ground G. The vertical magnet is thereby energized .twice and the shaft and shaft wipers 101, 105 and 106 are raised one step at a time until the shaft wipers .G circuit for the-` relay '50. extend-ing frorni i .thereby loc eser AvAiLAeLE C'oPi are carried up two steps opposite the bank levelln which are located the terminals of trunk lines leading to the repeater F Immediately following the last vertical impulse,` the rotaryimpulse spring is pressed onto the ground post 16, thereby energizing the rotary line rela-yg107 of the first selector E. The rotary line' relay energizes andplaees the springs 108 'and 99 in contact,whereby an Aenergizing circuit is` closed' through the private niagnet109. The pri-I vate magnet, as is Welll known', controls the side switch lWipersr 98, 110, 111 and 112.

The private magnet ,109, upon energizing and denergizing, permits the side switch Wipers to engage their respective contacts of the. second position, When the side switch wiper x12 engages the contact'point 113 an energizing .circuit is closed through the rotary magnetflll, said'circuit extending from groun'dlG through theside switch Wiper 4112, int rup'ter springs 115- and windings' of t rotary .magnet 111` to the' battery lead 69, thence through battery B to ground G. energizing,

- The. rotary magnet, upon Operates Wipers 104, 105 and 106 into vengagernent with the. first bank contact of the`. second' level. If the first contact is busya` positive guarding potential is present at the private bank Contact, and as soon as this Contact is vengaged by the Ashaft private Wiper `106 an' is established throu'ghthe private magnet-109 'from the groundedpri energizing circuit.

vate bank contactto' the private vWiper through the back-release relayll, side switch" b vwiper 111 (bearing'in mind 'that the side'l switch is'still in second position), through the private magnet 109 tothe battery leadA 169, thence through 'battery B to ground. G.

the side switch Wiper:111,:back-re1ease. rei lav-116 -to the shaft Wiper 106 -which engages the private bank "contact, L This guardingjiotential also. provides 'anienergizing ground through -theside switch-wiper, T111,` to the private wiper.'196,V ,throughthe relay tothe battlny lend 69 .thence through f batteryB to gre-und G. T e relay thereto rotate theV shaft side switch to pass' to third otentral'ts VevS- upon energizes and closes the arn'iature 5 1 in -contact with .the point 52, thereby bridging across the trunk conductors 122 and 123 Ythe impedance coil 53 in series with the springs 121 and 125. Although the relay 110 is included in this circuit it ribes not operatively energize, because it has a inw resistance, While that of relay 50 is comparatively high. The engagement of Upside switch wipers 93 and 110 with their third-position contact points extends the connection from the calling line through the shaft wipers 101 and 105 to the repeater F. An energizing circuit is immediately established through the line relays 37 and 38 and the Wi ings 39 and 40 of the double- -Wound coil^`1"`.`

ground G7 through the springs 119, 120 and 121, through the Winding 40 in, series with the rotary line relay 38 to the conductors 118,96 and thence through the subscrib-` ers substation to the vertical 'line conductor 2,9, trunk conductors A and 117, through the vertical line relay" 37 in series with the i lWinding 39 of the relay-4:1 to the battery The relay 41 being v'vound differentially This circuit extends from lead 69, thence through battery B to ground does not operatively energize; the line relays .37 and 38, however, the springs they control into contact. The .engagement of vthe springs 126 and 127 at thisfti-me v roduces no result. ,The engagegiiet '4 2 extending from ground G7 h'rough 'the 'springs 119 .and 120, through thm-springs 129 and'128, rotary magnet 42 faery. Blto ground G. The rotary magnet ,42 thereupon energizes and attractsits armaturei, thus rotating the ratchet Wheel 44 onestop.' It should. be stated in connec` operate and press ment of t e springs 128 and 129, however,-

Qvidesan energizing vcircuit. for the rotary to thev battery lead 69, thence .through battion with the repeater F that 'each time the repeater F isy Operated'the rotary magnet L12 denergi'zesjand energizes once foreach digit called. Hence, when .the ratchet Wheel 44 is given four steps the wipers 46 and 47 are carried: into engagement with the Contact `points 130 and 131, thereby providing a new brdgefacrossthe trunk conductors. 122 and 123. 'Ofcourse,it will-be understood'that this bridge connection is not complete until the 'last digit of the desired number is called.

.'lhe subscribersline conductors 29 .and .30

having been extended 'to the trunk conducitor's '.-117 and 118, the vertical line relay 3.7

position :tor'the second digit 2. The ener- `gizing circuit# 'through the vertical and.`

.'zrotay line relays 37 and 38'in series is ..broken[at"the substation A between the springs 31. and 32 when the dialis turned for the second digit 2. The rotaryli-ne relay.

Moles to normal 'positionbut-thef vertical line relay 37 senergized' tvv-ice on the is operated when the dial returns to lnormal l ias return motion of the dial. The energizing circuit extends fronrthe ground G through the groundfsprings 14 and l5, ground post- 16 and impulse spring 21 to the conductor 95, as` explained, side switch Wiper- 98, shaft wiper l04to the windin of the vertical line relay 37, Winding 39 of t e diii'erential re'l'ay 41 to the battery lead v69, thence through battery B and Vto ground G. The'winding 39 being included in this circuit, the differential relay 41 operatively energizes. The operation of' the vertical line relay 37 at this time, however, is without elect. The relay 41,. upon energizing, carries the' springs 121 and 124vout of engagement with the springs-120 and 125; also, the spring 121 is carried into contact with the spring 132. This disengagement of the springs 124 vand 125, as Will be seen, opens the bridge across thetrunkI conductors 122 and 123.- When the bridge including the' impedance coil 53 is closed across the trunk line conductors 122 and 123, anfenergizing circuit is proyided for the line relay.325 vof the selectorlswiteli N (Fig.'` 2). ground G20 through the Winding 320,side switch wiper 321, trunk conductor y123 to the `contact point 131, then through the springs 125 and 124, contact point 52, armature''l,

contact lpoint 130, 'impedance coil: 53, trunk conductor 122, side switch' wiper 322, wind!y ing 323 to the ,battery lead 138, thencel through battery'B toground G. Thelllfelay 325 thereupon energizes and 'carries .the spring 326 out of engagement withv the spring 327 andiinto engagement with the spring 328, thereby` closing` an -energizing circuit through the slow acting relay 329 extending from ground iGm tthrough the springs 326 and 328, sloivyacti-ng relay 329.-

to the battery ylead-138, thence through battery B ground G. The slow acting relay in', turn operates 4to carry the spring 330 out. of engagement Withthe spring 331 and into engagement with the spring 332. Thisis the ,condition'of the` selector-switch N, after the bridge has been closed at the repeaterfll prior tothe .sending of the impulses for the second digit. Noud,

when thefdifferential relay 41 of the repeater F'operates for ,then second digit and` opens tlieliridge circuit, between, the springs 124 and `125tivic'e, the, energizingeircuit for the linerelay of. the selector N` (Fig. 2) isibroken twice, and the ,spring326r falls hackA lltq .contact with thepspring 327 twice, thereby closing an energizing ,circuit This circuit` entends .freni grouiidg" G21 through .the springs' 326 an'df32f, springs This circuit lextends from differential relay 41. 'the springs 128 and 129 again closes an 337` arid two'steps in a; vertical .direc-r tion,V opposite the first coii'ta'ct` ofthe second bank level. After the impulses for the sec# ond digit have been sent, the, diterentialy 'relay springs 124v and 125 again Aresume 70` their normalfiposi'tions; thereby closing' an energizing circuit fo`r` 'the` line relay 325 of the selector N. The* relay A325 returns to its energized position, with the'spring 326 in contact with the spring 328, therebyl 75 again establishing an energizin'gci'rcuit for the relay 329. -The'relayy 329, kbeing slow acting, remains in its energized position While the impulses are being sent.' The private magnet relay 334,"ivhich is 'also slowl 80 tact. The engagement of these springs pro- `35 vides an energizing circuit for the private nia'gnet 341 `extending 'from groundv Gr21 through the springs 339 land 340, private magnet 341 to vthe battery lead 138,' thence through battery B to ground'G. The pri- 9g vate magnet vrelay 334-denergizes afterl the last' vertical impul'se, rsince this energizing circuit is no longer Amaintained after lthe l"springs 326 and 327 disengage; Hence, the

springs 339 and 340 restore to normal position, whereby theenergizing circuit for the private magnet 341 is in'turnbroken, which rivate magnet now dener 'zes' and 'ermits the side switch to :pass from `first tor wipers "335 and 342L engage the contact points 343 and 344, respectively. It should be explained thatfwhen the dial returnsto normal position afterbeing operated for the `second position, whereby the -side 'switch' 100 station A again close in contact. thereby providing the series .energizing circuit for the vertical and rotary lline relays 37-and 38 in series with, the windings 39 and 40 of the energizingcircuit*fonthe rotary magnet 42, therebygiving the ratchet wheel 44 a second step. The closure of contact between. the 1 3.43 prpvides an venergizing' circuit for the interrupter springs 346, rotary magnet 345, contact point 343, side switch Wiper 335l to.

-and'338 of the selector N into engagement with the first Contact of the second I. l level of the selectr banks. iii-oui'y which con- `1,25

tiict itis assumed the trunk line ifond'uctors 347. 348'and 349 lead 'to thel connector O.

' If the first trunk line is busy. however. and

the wipers have to pass over busy contacts,

The engagement of i Aside switch Wiper-:,335 and the contact point 115@` rotary magnet 345, from ground G20 to the Y i thebattery lead ,138. thence through battery 12o Bi'to ground nGr.. Thq said lrotary magnet tlen operates to rotate the shaftwipers 3,36,2 3.

switch C. rThis circuit extends from ground Gr24 through the 'Contact point 377, side switch wiper i'375,- springs 378 and 379, private wiper 370,bank contact 380 and relay 376 'to the battery lead 138. 4-The relay 376, upon energizing, disconnectsthe-switch C from thecalled line to prevent the operation of the switch when the called subscriber answers. l i

l'LYhen the side switch wiper 367 lof the connector engages vits third-position contact point a cirpuit is closed through the ringer relay 381. j This circuit extends from ground G25 through the interrupte'r382, springs 383 and 381, ringer relay 381, side switch wiper' 367 and relay 366 to the battery lead 138, The ringer relay 381, upon energizing, op-

erates to disconnect the calling line and to bridge the generator L across the calledr line to signal the called subscriber. Since the circuit lof the ringer rrelay 381 includes the interrupter 382 therelay will be eneri gized only intermittentlyso as not to ring 4 the bellslatthe substation A continuously..

When the subscriber at substation A re-- moves his receiver -inresponse to the signal a bridge is closed across the line through the transmitter and receiver, as previously l explained. `lVhen this bridge is closed across the line, or as soon thereafter as the ringer relay 381 denergizes, the substation is provided widi.A talking battery .current over a circuit extending from ground G24 through the side switch wiper 377 Winding 385 of the back-bridge relay 386, ringer-re.

lay springs 388 land 389, side sia'itch Wiper v374, shaft `wiper 369,. lineconductorl310.,

thence throughthe substation A and back over the'line 309, wipers 368 and 373, springs 39Oaudl 391 and throughthe winding 387 of the relayy 386 t'o the battery lead The relay 386 is energized 'by the 138. closure ot thiscircuit and, by separatingthe springs 383 vand 384C, ,prevents further energization of the relay 381 after the called subscriber has answered. Thetalking circuit between the two connected, substations is shown in heavy lines in Figs. 1 and 2. y

When the dial returns to its normal position after the last digitt() the rotary magnete-2 of the repeater. F operates to carry the wipers L16"-and 47 into `,engagement with the contact points 130 and 131, thereby bridgingl the impedance coil 53 across the trunk con- 4 and' the diiferential relay-41. whereby the bridge across the line'condu'tors 122 and' 123 would be broken, and the switches might 'be released if the button was pressed for too long a time With the impedance coil 53bridged across the trunk line conductors y122 and 123, independent of the operating relays, this exigency is provided for.

The release of the central oiiice switching apparatus occurs when the calling subscriber restores' his receiver to the switch hook, whereby the camarm 4 presses the v release springs 7 8 and 9 into contact simulv taneously,` thereby grounding the l1ne conductors 29 and 30.A The ground to the line conductors 29 and -30 imbalances the differential relay 41',-whereby.the said relay now energizesQand presses the spring 121 tery lead 69 instead of ground G7. When'A the contact betweenV springs 119 and 120 is broken the circuit through the rotary magreturn to its normal position when thear mature. 4:9- is withdrawn bygthe magnet 48.

When the spring121 engages the spring 132 .net42 is'opened, thus allowing the armaand the relays 37 and 38 are'alsoenergized,

an energizinofcircuit is established through the relay 48 extending' from ground G17,

and 127, relay 48 to the springs` 132, and 121,.

lthrough the side switch ,wiper 11-1.ogtthe .i 'selector switch E,bac krelease relay. 116, jl shaft wiper 106, through the springs- 126 100. y.

to the battery lead ,69, thence through bat; u f.

'14. The ratchet-wheel thereupon restores 116 Vot" the selector .E, beingI included in teryl B to ground Gr.v The relay' 48..there-` i r`uponenergizes and attracts its armature@ .out of engagement with' thewratchet wheel this circuit, also operatively energizesandvv 1i-m presses the springs 252 and'253 into conf" tact, whereby an energizingcircuit is estabthe'selector switch E. The-release magnet..` .1'

11a-1,., lished throught-he release-magneto 254;.,energizes and in turn. closes engere' y i Lgizing circuitwthrough the releasefmagnet ..79 of the line switch C. VThis circuit ex-ztends from ground. ithrough, the' ContactA point 255, spri'ng3256, b ank springs77 aIdJj,- i 7 8, release magnet 79 tothe battery lead 69,

thence through battery B tofground Gr." All of the relays and magnts 'thus energized.y

switcheswhen the ground co"ImectionytotheI stores to'v normal position tthe'shaft wipers contacts, and the energizing circuit through the relay 50 of the repeater F is broken.

l12o` attract their respective armatures .y and rell f main 1n readiness to restore the1rzrespect1v The armature 5.1 therefore disengagesr` from the contactfpoint .52,A which preyents ther closureof vthe bridgeacross the'trunk when the relay 41 again denergizes.

`` The opening `of the bridge across the trunk conductors 122 and 123 bythe restoration olfA the wipers 46' and 47 of the repeateirl permits the line relay of the connect-or yto de'energize and open the energizing circuits vof the release relays 3:57 andv 329,101,,thenswitches O and N, respectively. Although. it has not been previously mentioned,-it is evident that. after the connector side switch reaches thiid position theA holding;- ground of the release relay 329 of the selectorN is `shiftedtrom ground- Grt3 to ground k(i122 throughthe wiper 363 and springs 354 aud356. Thus, the denergization of the-"relay 353 breaks the circuit oi both release relays,.as stated. When the relays3j57 andv 329' deiiergize they close the energizing circuits ofthe. release magnets 392"'and 393. respectively.'.'The circuit of thei'fcori'nector release magnet 392 extendsA from"groundr G22-thiough springs 354 and 355, '3`59 aiid1 358, magnet 392 and oil" normal sp'ring's'394 and 395k to battery lead 138.

The. release magnet 392 u on enereizin releases the mechanism of the connector O, l wing'itto be restored to normal position. Then the' switch shaft reaches its lowest vv@'toallow`it -to=be restored to the yline of substationAf.A The central otlice switching mechanism is thus restored to 'normal position and lremains in readiness to be used by anotherxcalling subscriber.A

y The foregoing is a description of how a subscriber of a .three-wire exchangelmay obtainconnection with a subscriber of a two- Wiregexchange., -lt will now be explained how' a call proceeds inthe opposite direction,

'Y orhow the subscriber at substation A can call substation A (#4440). The engagement oi thesprings 300 and 302 at substa. tion'A," upon the removal of the receiver, closesan energizing'fcircuit through the trip `magnet 397 of thelin'c switch C. This circuit extends from ground G2G-'through the magnet-397, springs 398and 399,1ine 310,

springs 300 and 302, impulse springs 308 and I307, receiveij 306, transmitter-305, line 309,

*springsy 401 v and 400,. resistance 402 and springs 403;"and y404to'ljattery lea d 138. The trip magnet 397, uponenergi'zing, causes the lswit'cgh C' to operate in the same manner` as explained torithe switch C to extend the connection over the trunk conductors 405 and 40G tol the selector H (Fig. 3). ,pperation of the switch C also closes a circuit through the in'aster switch relay 317 'in the saine manner in whichthe circuit was closed 'through the winding 72 of the relay 70 of master switch D (Fig. 1). The relay 317,

upon energizing, closes an energizing circuit,

through the rel ay 408 and motor' magnet 319. This circuit extends from ground G27 tiple, interrupter springs 409 and; spri'ngs 410 and 4,11 of relay 317 to battery lead 138. Since this circuit includes the interrupter springs 409 the motor magnet 319 begins to operate in a manner similar to that 0f a buzzer to give the ratchet wheel 313 a continuous step by stepinotion to move the idle plungers away from the trunk just seized.

-through relay 408 and magnet 319 in mul- As soon as the wheel 313 moves one step the notched wheel 314 forces spring 315`into engagement with spring 316 to maintain the circuit of the motor magnet 319, independent oi' relay 317. lVhen the master Switch has advanced a short distance farther, the Wiper 318 leaves the contacfr 412, but the motor magnet continuesto operate until the spring 314 and disengages spring 316, by Which-fy timethe plungers will havereaclied a position-directly in front of the next trunk. If i the next trunk is busy, however,the relay 317 remains energized, when the wiper 318 passes onto the next contact and causes the plungers to be carried past the busy trunk to the next one which is idle. The relay 408 is nergized when Aits circuit is first closed by relay 317, but being slow acting does not have time to denergize during theinomentary interruption ot itscireuit at the springs 409 while the magnet 319 is operating. Thusrthe relay .408 is energized during the entire time the master switch is rotatig, and Operates to disconnectl the battery from the trip niagnets 397 of all line switches C,' and'con nects the busy signaling machine M with' the idle lines through Athe 'resistance 402 and springs 400 and 401. Thus, any subscriber who attempts 'to make a call while his master.

switch is operating will not only be unable" to operate his line switch, but will receive the busy signal as well. v

When the connection is extended tothe.

selector H by the line switch C the linerelay 133 is energized over a circuit extendingtroni ground (1 `through winding 134, side switch wiper135. trunk conductor 406, line 310. through substation Afiand back over line '309, trunh 405. side switch wiper 136 A. .lgs fry? .y l ie a l p ipon eneigi/,ing c oses a circuit through th `lcasef relay 142 in the saine manner explained for the relay 329 of segino 137 to battery lead 138. -The lector N. Vhen the calling device is oper' l ated for the first digit (4) four impnlses are transmitted to-the line relay 133. The selector H operates in the same manner as .9g v315 drops into the next notch of 'the wheelsecond digit 4 the bridge across the line conexpiained for the selector N, except that sim-c the digit called is 4 the shaft 1s raised tour steps by the vertical magnet 146, after which the rotary magnetl automaticallyl rotates the wipers 149, 15()a and 151y onto the terminals of an idle pair of trunk conductors 157 and 158 leading to a repeater I. The private magnet relay 147 operates in the same manner as the relay 334 of the selector N to cause the private magnet 151 to trip the side sn'itch from first to second position after the vertical magnet has operated. At the inst-ant the connection is extended to the repeater I by the selector H the relay 54 is energized in the same manner as was the relay 133 of the selector H when the connection was first extended to it by the line switch Cf. The relay 54, upon energizing, operates to; shift the spring 163 out of engagement A.with the spring-164 and into engagement with the spring 165, and to torce the springs '166 and 167 out of engagement with the springs 168 and 169, respectively. The engagement of the springs 163 and 165 closes a circuit extending from ground GW through springs 163 and 165 and relay 57 to battery lead 138. The relay 57, upon energizing, forces springs 170, 171 and 172 into engagement with the springs 173, 174 and 17 5, respectively, whereby the spring 164 of relay 54 is connected with the vertical trunk conductor 178, relay 58 is connected with battery lead 138, and a holding circuit is closed through the release relay 142 of the selector H. This circuit extends from ground G through thel springs` 175 and 172, private wiper 151, conductor 160, side switch wiper 152, contact point 176 and relay 142 to the battery lead138.

iifhen the calling device is operated for the ductors 399 and 810 is opened .four times, each time allowing the relay 54 of the repeater to denergize and permit the springs 163, 166 and 167 to Vreturn to normal position momentarily. The engagement of the springs163 and 164 closes an energizing circuit for the vertical line relay 177 of the selector switch J (Fig. 4); This circuit ex-v tends from ground G10 through the springs 163 and 164, springs 170 and 173 to the vertical trunk conductor 178, side switch wiper 179' (Fig. 4), vertical line relay.177 to the battery lead 180, thence through battory B to ground G. Also, when the spring 166 engages the spring 168 an' energizing circuit is closed through the slow acting relay 58 extending from ground (lr10 through the springs 166 and 168, relay 58, springs 171 and 174 to the battery lead 138, thence through battery B and to ground G. The relays 57 and 58, being slow acting, remain in their o erative position 4until all of the impulses or the third digit have been sent. The relay 58, upon energizingpoperates to close the springs 181 and 182 in ;contact, whereby a circuit is closed throu hthe re` lease relays 59 and 60. This circu t extends from ground Gr12 through the springs 181 and 182, quick-acting release relay 59 in series with the slow-acting release relay 60 to the battery lead 138, thence through battery B to ground G. The relay 59, upon energizing, attracts its armatures 183 and 184 out of engagement with the contact points 185 'and 186. The relay 60, upon energizing, attracts its armatures 187 and 188 into engagement with the grounded contactpoints 189 and 190. This is the condition of the repeater I while the impulses for thesecond digit 4 are beingl transmitted. The vertical y line relay 177, upon being energized four times, operates to close the springs 191 and 192 in contact, thereby in turn closing an energizing circuitthrough the vertical magl net 193, whereby the shaft Wipers 194, 195 and 196 are carried four steps in a vertical direction` opposite the first contact of the second level of the selector bank. After the dial at substantion A4 returns to normal position for the second digit 4, the springs. 166 and 168 remain out of engagement,'thereby breaking the energizing circuit for the slow acting relay 58. The slow acting relay 58 in turn restores to normal position, permitting the springs 181 and 182 to disengage, there-l by breaking the energizing circuit for the release relays59 and 60. Wheny this occurs the armatures 183 and 184 of the quick acting relay 59 immediately restore-to normal position in engagement with the contact points 185 and 186', respectively. The armatures 187 and188 of the lslow acting relay 60, however, remain in contact vwith the points 189 and 190,' respectively, for a moment. This operation produces a ground impulse for the rotary trunk line conductor 194, there- Vby providing an energizing circuit for the rotary`line relay 197 of the selector switch J. No ground'impulse, however, is transmitted to the vertical trunk line conductor 178, since the springs 167 and 169 are disengaged. The energizing circuit forthe rotary line relay 197 extends from ground G through the Contact point 190 and armature 115 188', cont-act point 186 and armature 184 to the rotary trunk line conductor 194, side switch wiper 198 (Fig. 4), through the rofrom first to second position, whereby anen- I ergizing circut'is established through the rotary magnet 201. The rotary magnet 201 now operates to rotate the shaft wipers 194,

195 and 196 in a rotary direction to select an idle trunk line leading to a connector rfour times, as explained. The relay 54 oper Lampes f j `switch K. Aiterthe rotary magnet ceases to operate, and the side 'switch wipers pass to third position, af-[guarding potential is y established at the private bank contact engagedbythe shaft wiper 196 for protecting the seized trunk line conductors 202 and 203 against seizure by any othercall-ing subscriber This potential. extendsfronn ground G14 to the side switch wiper 204, back-release relay 205 to the shaft private wiper 1,96, which latter engages the private bank contactcorresponding to the trunk line conductors v202 and 203. The operatioin of they dial for the last two digits is eiiect'ive in operatingthe vertical and rotary line relays 206a11d 207 of the connector switch K. The operation of the substation calling device for' the third vdigit 4 again opens .the bridge across the li'ne four times, thereby in turn operating the line'relay 54 of the repeater I altesto send 'four ground im ulses to the vertical trunk vline conductor 1 8, which are ef- :fective inclosing an energizing circuit for the vertical line relay 206 ofthe connector switch K. This circuit extends from ground G19 atthe'repeater l tothe springs 163 and 164,`springs 170I and 173 to the'trunk conductor178, side switch wiper 179l (Fig. 4), shaft wiper 194,"trunk conductor 202, vertical lline relay 206, winding 208 of the diferentialrelay 209 to the battery lead 180, 'to ground G.

thencethrbugh battery B `to `groundfif The winding 208 .being included'in this circuit', the relay 209 voperativelyy energizes, but its operation atthis time is without effect.. The

relay l206 'thereby closes thesprings 210 'and 211 into contact, whereby tour impulses are acircuit extending from ground Gr15 through the springs kv211 and 210, springsv 213 and 1 214 to the side switch wiper 215 and vertical magnet 212-to the battery vlead .180, thence through battery B and to' ground G. The shaft wipers 216, 217v and 218 are thereby raised to the' fourth level opposite the first contact. When the dial returns to rest after i having sent the four impulses, the line relay 54 of the repeater I returns to its normal,r energized position and again breaks the cnorgizi'ng circuit `for ,the slow acting r.. Lay

58. whengthey springs'l and 168 disengage. The springs 181/ and 182 again operate, as before, `periritting `-the release relays 59 and 00. tor'estorefto normal positiomwhereby a rotary impulse is transmitted t the rotary trunk conductor 194, as previously eX- plained., This impulse provides' an ene'rgiz ing circuit for the rotary line relay 207 eX- tending iromgroundG13 tothe. trunk conductor 194, as stated, through the Vside switch wiper 198,' shaft wiper 195, trunkconductor j 203 lto the rotary line relay 207 and wind-' ing 219 of the diiierential relay 209, through the sf'fngs 220 and 221 t'o the battery lead cuit,` as is the winding lay 209 operatively energizeabut its operation at this time is also without effect. The

in the circuit of' the rvertical line relay 206, the differential rerotary line relay, upon energizing, presses the sprino's 222 and 211`1nto Contact, thereby closing an energizing circuit forthe private magnet .from ground G15 through the springs 211 andf222, winding of thefprivate magnet 223, springs 220'and 221 to the battery lead 180. thence throughbattery B to ground G. rlhe private magnet 223 now 'operates to permit the side. switch wipers to -pass from first to second position.v lVheii'the dial. is turned Jorthe'last digit 0 the vertical line relay 206 of thejconnector K is operated ten times, in the manner previously explained. When the vertical line"` relay ticalrnagnet 2'12, since the side switch wiper 215 isf-now in second position, 1n engagement with the. contact point 225. Thiscircuit eX-v tendsfrom ground G15 through thesprings f 211 and 210, privato magnet springs 213 and 214, side switch wiper 215` contact point 225,

winding of the rotarymagnet 224 to the battery lead 180. thence through' battery .B

The 'rotary' magnet now oper-A ates to rotatethe shaft wipers 216, 217 and 218 vten steps in' a rotary or circular direci f 1002...' contacts comprising the terminals"ofthel tion and into ,engagement 'with' the. bank normal conductors 226t 227 and. 91vv of`-'th.e i

line of substation #4440. When the linef. I transmitted to the vertical magnet 212 over relay 54 of the repeater I returns to its energized position the circuit to thefrelay .581 is broken, and the release relays 59 and 60 again operate to provide anenergizing cirexplained@ The rotaryline relay'207 oper: ates in turn to close 'an energizing circuit through the private magnets 223.whic'h also operates and permits the side switch wipers` to pass from second to third position. lVhen the side switch wiper 215 reaches third `position the ringer relay 220 is placed under the control ofthe vertical relay 206 andat the Sametime the connection is completed with thecalledline by the side switch wipers 248 wiper 239 with its third-positief` Contact point provides a guarding potential jfor the and 413. The engagement of the side` switch..v .1201

connector private bankcontacts of the called j line and closes anenergizing eircuitlfor the cut-ofi' relay 92 :of the line switch ,Cl This` circuit extends from ground G16 throughthe side switch wiper 239, private -wiper 218,

connector private bank4 contacts lof' called line, conductor 91-and relay 92tobat# tery. The relay. 92, upon energizigvdi connects the trip magnet 6l `from thejegnd operates for the last digit, however, an ener# gizing circuit is established through the rotary magnet 224 instead of through the verline, and by closing the contact between the springs 93 and 94 connects the line conductor 30 with its connector bank contacts.

In order to signal the called substation, the calling subscriber againoperates his calling device, preferably for the digit 0. The repeater I responds to this operationof the calling device to again repeat a seriesof ground impulses to the vertical trunk conductor 178. The vertical relay 206 and differential relay 209 respond to these impulses in the usual manner, but in this instance the engagement of springs 211 and 210 closes an energizing circuit for the ringer relay 226. This circuit extends from? ground G15 through springs 211 and 210, 213 and 214, side switch wiper 215, contact point 231, relay 226;` and springs 261 and 250 to battery lead 180. The relay 226, upon energizing, operates to disconnect the calling line and to bridge the ringer generator .L across the called line to ring the bells at substation A. The rotary' impulse following this last series of vertical impulses causes the operation of the rotary relay 207 and private magnet 223 in the usual manner, but this operation is without effect, because the side switch has .already reached the limit of its travel.

When the called subscriber removes -his receiver in response to the signal the springs 31 and'32 engage,.thereby closing a circuit over which the substation A receives talking current. This circuit extends from ground Gr1a at the connector K through the side switch wiper 239, winding 240 of relay 238, ringer relay springs 241 and 233, wiper 217, conductor 227, springs 94 and 93, line 30, primary-winding 19, transmitter 17, springs 31 and 32, line 29, conductor 226, wiper 216, side switch wiper 248 and winding 249 of the relay 238 to the battery lead 180. The relay 238 is energized by this talking current, but has no agility at this time.

After the conversation is completed the central office apparatus is released by the restoration of the receiver at the calling substation, as in the previous case, but in a slightly different manner. When the springs 300 and 302 at substation A are separated by the switch hook the circuit of the line relay 54 of the repeater I is broken. This relay, upon denergizing, permits the springs 163, 166 and 167 to restore to normal position, thereby closing an energizing circuit through the relay 58 extending from ground G10 to the springs 168 and 166, relay 58, springs 171 and 174 to the battery lead 138, thence through battery B to ground G.

- The relay 58 thereupon energizes and closes the springs 181 and 182 into contact, whereby the circuit throughthe release relays 59 and 60 is again established. When the springs 163 and 165 disengage, the energizing circuit for the slow acting relay 57 becomes broken and this relay in turn restores to normal position, permitting the springs 170, 171 and. 172 to disengage from the springs 173, 174 and 175. This disengage- 4ment of thesprings 172 and 175 breaks the shaft to normal position. When the switch y shaft reaches normal position the normal arm 260 carries the spring 259 out of engagement with contact point 258, thereby breaking they energizing circuit of the rey lease magnet 257. The engagement of springs 143 and 144 closes a second circuit extending from ground G through springs 139 and 140, 143 and 144, relay 414, springs 415 and 416, conductor 407, bank springs 417 and 418 and release magnet 419 of the line switch C to the battery lead 138. Both the magnet 419 and the relay 414 are energized over this circuit, the magnet 419 placing the mechanism of switch C in position to be released by the subsequent denergization of said magnet, lwhile the relay 414 opens the circuit through itself and the magnet 419. The magnet 419 thereupon denergizes, allowing the line switch C to be restored to normal position. The circuit of the magnet 419 is not again closed when the relay 414 denergizes, because bank springs 417 and 418 ,age then separated. The relay 414 is made slow acting to pre ent its denergization before the switch C has released.

The disengagement of springs 171 and 174 of the repeater relay 57 opens the circuit through the slow actingr relay 58A which, after a moment, denergizes, thus permitting the springs 181 and 182 to restore to normal position. The opening of springs 181 and 182 breaks the circuit through-the release relays'59 and 60. Relay 59 immediately denergizes, while the slow acting relay 60 remains energized for a moment, thus lgrounding the vertical and rotary trunk Leashes line conductor 194 extends from 1ground G51 to the armature and contact points of the release relays, as before explained, to the 1 tru l; conductor 194, side swich Wiper 198 '(Fig. l), conductor 203, rotary relay 207,

through the winding 219 of the relay 209,

through the springs 220 and, 221 to the bat-` tery lead 180, thence through battery B to ground G. The vertical androtary'line re-n lays thereupon energize, and also the dierential relay 209, since the windings 208 and 219 do not oppose one another when. -thus carrying current. The spring 250 is there fore shifted vout of engagement with 'thespring 2-'l9a and into engagement With the spring 261. It will be seen that the closure ot the above circuit for the rotary relay is dependent upon the back-bridge relay 238 being denergize'd. If thecalled subscriber has not hung up his receiver, the circuit ot this 1elay will be broken by the separation of the springs 249 and 250 of the relay 209,

4which is energized'through its Winding 208A -lay 205, shaft private wiper 1.96,"through .the springs 262 and 263, release magnet 264, differential relay springs 261 and 250 to the battery lead 180, thence through battery B to ground G. The release magnet 264, kupon energizing, operates to restore the connector` side switch wipers and switch shaft wipers to` normal lposition. The release relay 205 of the selector switch J, being included in this release circuit, also operatively lenergizes and presses the springs 265 and 266 'into contact, thereby providing a circuit for the release-magnet 267. The release magnet 267 energizes and remains in readiness torelease the selector switch J when the energizing circuit for the release relay 205 is broken. The .slow acting release relay of the repeater I, after a moment, is restored jto normal position, thereby disconnectingv the trunk conductors `178 and v194 `from ground'Gla.

stored, leaving the central oitice apparatus inl normal position and in readiness to be;

used by another callingsubscriber.

From the foregoing it will be seen that I i, provide eflicient means for lcarrying on Vtrunkin'g from a three-wire to a two-wire 'system, and. `vice versa, and that this is ac complished through the drnedilniri ofthe repeaters F -and I, as previously explained. As'herein disclosed, these repeateraareemployed4 in connectionI with automatic con' All of the release relays and i ymagnets thus involved in a release are rel' nectors for finding the called lines, and in combination with means wherebyva calling subscriber may, without the assistance of ,an operator, extend connection-to said. automatic connectors. In other wordsyanld as herein disclosed, no switchboard.operators are necessary, as the connection from'a calling line to a called line, is entirely-automatic. It will beunderstood, howev I do not limit myself to this particular kind of a system, as .theserepeaters .F and A,Iv-'may be employed in other systems, and in conjunction with 'manual apparatus, :"without departing from the spirit or my invention.

It will 'also be seen that, with my"improved construction 'and circuitarrange unent, the calling subscriber' signals* the called subscriber when the call is r-frolnia two-wire subscriber to a' three-.Wire subscriber by an additional movementof" the dial at the calling substation. r For-thepurpose of this application '5I desire to define the meaning of certainv terms or expressions as follows: VBy ay thre'elwire line circuit, or three-wire automatici subscribers telephone line, I mean @af line Y which must be grounded at thesubstation thereof` in order tocontrol the automatic switching apparatus at the exchange oneentral. station. By a two-wire line, rftwo Wire line circuit, or'equivalent expression,

I mean a line the two sides owhicli are necessarily employed in series to 'controlthe automatic apparatus Aat the exchange or 'central station, no ground being employed at' thesubstation .of said linej By thecxpression repeater, I mean amechanismfgofany suitable character which isiadaptedltoyre ceive calling` impulses, and to then repeat o1; transmit duplicatespf said'- impulses in the direction' of the called subscriber. What' I claim as my inventionis'-:'f a'.

1. In a telephone system, means" for ""that:

transmitting calling impulses, andfaj` repeater for receiving and .repeatingsaidjimpulses, said repeater provided with Aparallel voice-current conductors, a stepsby-stepj' operated switching mechanism, said mecha nism responsive to said impulses, andfmeans operated by said mechanism toA form a bridgev between said voice-current con- Y ductors. Y 2. In a telephone system, means for trans#y mitting calling impulses, and afrepeate'rlifor receiving and repeating said 'impulses,-said `repeater provided with parallel voice's'curf vrent conductors, a ratchetmechanismg'acre f lay for operating said' ratchet mechanism;

whereby a plurality of Aactuation's ofsaidmechanism will close a bridge'betwee said Voice-current conductors.- .I s n 3. Ina telephone system, Ymeansaffoirtransmitting calling impulses, and re-4 peater for receiving and repeatingzsaid impulses, said repeater provided with parallel voicecurrent conductors, a step-by-step operated switching mechanism, said mechanism responsive to said impulses, means operated by said mechanism to form a bridge between said voice-current conductors, and

- means including-a release magnet forrestoring saidlmechanism to normalposition.

r4:."1'11 a telephone system, means for transmitting calling impulses, and a repe'ater for receiving and repeating said irnpulses, said repeater provided with parallel voicefcurrent conductors, aA ratchet mecha- Y. nism, a relay for operating said ratchet mechanism, responsive to said impulses, means whereby a plurality of actuations of said mechanism will closea bridge between 'said' voice-current conductors, and means slow-acting relays, and a ground connection controlled by one of said second pair of relays.

6. In a telephone system, means for transmitting calling impulses, a repeater for receiving and repeating said impulses,. an au- 'tomatic switch whereby the calling subscriber connects with said repeater, said repeater provided with parallel voice-current conductors, a step-by-step-operated swltching mechanism, said mechanism responsive -to said impulses, and means operated by saidfmechanism to form a bridge between said voice-current conductors.

7. In a telephone system, means for l transmitting calling impulses, a repeater for receiving and repeating said impulses, an automatic switch whereby the calling subscriber connects with said repeater, said repeater provided withl parallell voice-currentconductors, a ratchet mechanism, a relay for operating said ratchet mechanism, responsive to saidV impulses, and means whereby a plurality of actuations of said mechanism will close a bridge between said Y- voice-'current conductors.

8. In a telephone system, means for transmitting calling impulses, a repeater for receiving and repeating said impulses, .an automatic switch whereby the callmg subscriber connects with said repeater, said repeater provided with parallel voice-current conductors, a step-by-step-operhted switching mechanism, said mechanism responsive to said impulses, means operated by said mechanism to form a'bridge be tween said voice-current conductors, `and means including a release magnet foiresaid mechanism to normal pos1t1on.

9. In a' telephone system; l means for transmitting calling impulees`,. a repeater for receiving and repeating said impulses, an automatic switch whereby thev calling subscriber connects with said repeater, said 7G repeater provided with parallel voicecurrent conductors, a ratchet mechanism, a relay foroperating said ratchet mechanism, responsive to said impulses, means whereby a plurality of tictuations of said mechanisml'z will close a bridge between said voice-current conductors, and means including a release magnet for l.restoring said mechanism to nonnal position.

10. In a telephone system, means for trans Se mitting calling impulses, a repeater having a pair of relay coils for receiving said impulses,slowactin relays controlled by said first-mentioned re ay coils, relays controlled in series by one of said slow-acting relays, a

ground connection controlledby one of said lastmentioned relays, and am automatic I switch whereby the calling subscriber c0n nects with said repeater.

1l. In a telephone system, mearis for trans1 mitting calling impulses, and a repeater for receiving and repeating said impulses, said.,l

. rent conductors, a ratchet mechanism, a relay for operating said ratchet mechanism, responsive to said impulses, means whereby a plurality of actuations of said mechanism will clos a bridge between said voice-curv rent con uctors, andan automatic switch for finding the called subscribers line. 13. In a telephone system, means for transf mitting calling impulses, and a repeater for receiving and repeating said impulses, said repeater provided with parallel voice-current conductors, a step-by-step-operated switching mechanism, said mechanism responsive to said impulses, means operated by said mechanism to form a bridge between said voice-currentv conductors, means including a release magnet for restoring said mechanism to normal position, vand an automatic switch for nding the called subscribers line.

14. In a telephone system, means for transmitting calling impulses, and a repeater `for receiving and repeating said impulses, said repeater provided with parallel voice-eurrent conductors, a ratchet mechanism, a relay` for operating said ratchet mechanism,

liu

responsive to said impulses, meansV whereby a plurality' of actuatioiis of said mechanism will close a bridge between said voice-current `conductors, means including a release magnet for` restoring said mechanism to normal position, and an automatic switch for finding the called subscribers line.

In 'a telephone system, means for transmitting calling impulses, relay coils for re- -called subscribers line.

ceiving said impulses, slow-actii'ig -relays `'controlled by (said First-mentioned relay coils', ,relays controlled in series .by one of said slow-acting relays,a ground connection "controlled by one of said controlled relays,

and an automatic 'switch for finding the 16.` In a telephone system, .a three-wire circuit, a` two-wire circuit, means i:or transmitting calling impulses, and mean., for repeating said impulses from vthe three-wire circuit to/ the two-wire circuit.

of, .a called telephone line, another automatic l switch, a repeater between said automatic progress of thelca'll from the calling line to switches, a metallic linecircuit over the two. .sides of which said repeater controls the said last-mentioned automatic switch during the the called line, andmeans whereby lthe sub- .scri'ber of said called line may callthe subl trollable over the two sides of the called line in series when the latter used as a calling lays.- for repeating impulses oversaidoutmatic subscribefs' line', andl means includ scriber of said calling line, said means including one or more automatic switches conline. "18.In a telephone system, an automatic switch, a line circuit for said switch, means for controlling said switch. by grounding first one'side and vthen tlie`other of said line circuit, a second automatic switch, a trunk line circuit for sa id second automatic switch, a repeater Iadapted -to control-the said second automatic switch over the two sides rof the trunk line lcircuit in series, and means for connecting the first lautomatic switch with tliesaid repeater.

19. In a telephone system, a three-wire automatic subscribes lin-e, atwoewire autoing a repeater? for extending connection from the three-wire line to the two-wire line. 20. In a 'telephone system, a two-wire automatic subscribers line, a three-wire automatic. subscribers line, and means including a repeater for extending connection 'from the-two-wire line to the three-wire line.

21.111 `a telephone system, an automatic switch, a line circuit .for said switch, .means `'orcontrolling saidswitch over the two sides ofk said line circuit `inuseries, a repeater, means for connecting said -switcli with the said. repeater, a second, automatic switch,

and a trunk line circuit itorV said second .automatic switch,- said -repeateradapted to.

control the'said second switch by groundingirst oiie side and then 'the other of said trunk line.' y 22. In a telephone system,-a calling telephone line, an automatic switch,means for controlling said automatic switch over the two sides of s aid telephone iine in series, a repeater, means for connecting f the said switch with the said repeater,.a second au tomatic switch, a trunk line circuit for. said second automatic switch, a calleditelephone line, and one or more other automatic switches controllable by grounding the called line at the substation thereof when this lin'eis to be used as a calling line said repeater being provided with means for grounding the said truck line to control the second automatic switch during` the progress of the call from ,other telephone lin '23. In a telephone system, a circuit, means for grounding' said circuit to transmitcallf ing impulses over the same, another circuit, and means for receiving said impulses and repeating the same over the two sides vofv said second circuit in series.

24. In' a telephone system, a trunk line, meansfor transmitting impulses, a repeater fr repeating saidiinpulses, said repeater indii:

l the first-mentioned telephone line to the' `means controlled by said second' pair otregoing trunk. l

trunkv circuit', means for transmitting impulses by grounding first one side and then the other ofsaid line circuit, and a repeater for receiving said impulses and' for repeating them over two sides' of the trunkjcirciiit e receiving said impulses and" for1repeatingtA `them over two sides of thetrunk circuit in' series,y said repeater comprising a pair of line relays and. a double-'wound relay,"feach of said line relays being connected in series with one winding of said double-wound relay, a step-by-step switch, and 'a release ref lay therefor, said release relay being connected in series with oneof'said 'line relays.

27. In a telephone s stem, aline icirciiit,

25. In a telephone system, a line Circuit, :aj:

with' one winding of said double-wound a calling device, a stepy-step switch,

for operating said calling device 'to transmit impulses over said line circuit, means for Aa trunk circuit, a switch for extendin a connection from said line circuit to sai trunk circuit, a bridge across said trunk clrcuit,

" 'a step-by-step switch for controlling normally open contacts in said bridge, a relay for controlling said bridge at another point, and means for energizing said relay when connection is extended to said trunk circuit.

29. In a telephone system, a line circuit, a trunk circuit, a switch for extending a connection-from said line circuit to said trunk circuit, a repeater for repeatin from said trunk to a second trun a bridge across said second trunk circuit, a step-byep switch for controlling normally open contacts in said bridge, a relay for controlling said bridge at another point, and means for energizing said relay when connection is extended to said trunk circuit.

30. In a telephone system, a pair of trunk circuits, a repeater for receiving impulses from the first of said trunks and repeating L iem to the second, said repeater includin",r a pair of line relays, a stepby-step switch, an operating magnet therefor controlled by said line relays, and a bridge across said second trunk controlled by said switch.

31. In aftelephone system, a pair of trunk circuits, a repeater for repeating impulses from the first of said trunks and repeating them to the second, said repeater including a pair of line relays, a step-by'step switch, an operating magnet therefor controlled by said line relays, a bridge across said second trunk controlled by said switch, and means for operating said switch when the impulsetransmitting means returns to normal position.

32. In a telephone system, a repeater, circuits, an automatic switch for connecting .the circuits with the repeater, means for sending impulses first over one circuit and then over the other, an auxiliary circuit associated with the repeater, and means in the repeater for receiving said impulses and repeating,r them to the Isaid auxiliary circuit over both sides of the auxiliary circuit in series.

33. In a telephone system, a repeater, circuits, an automatic switch for connecting the circuits with the repeater, means forv sending impulses tirst over one circuit and then over the other, an auxiliary circuit associated with the repeater, and means in the'repeater for receiving said .impulses and repeating them to the said auxiliary circuit.

impulses and means in said repeater for holding said auxiliary circuit closed after the impulses.

34. In a telephone system, a repeater, circuits, an automatic switch for connecting the circuits with the repeater, means for sending impulses rst over one circuit and then vover the other, an auxiliary circuit associated with the repeater, and means in the repeater' for receiving said impulses and repeating them to the said auxiliary circuit, and a bridge controlled by said repeater for closing the auxiliary circuit.

35. In a telephone system, a repeater, circuits, an automatic switch. for connecting the circuits with the repeater, means for sending impulses first over one circuit and then lover the other, an auxiliary circuit associated with the repeater, and means in the repeater for receiving said impulses and repeating them tthe said auxiliary circuit, an automatic switch connected with said auxiliary circuit and operated by said im pulses, means in said switch for releasing the same controlled over said auxiliary circuit, and means in said repeater for preventing the release of said switch.

36. In a telephone system, a repeater, circuits, an automatic switch for connecting the circuits with the repeater, means for sending impulses first over one circuit andthen over another, another automatic switch for extending the connection beyond said repeater, a circuit in said other switch for con-- trolling the operation thereof, and means in said repeater for receiving I said impulses and repeating them over both sides of said controlling circuit in series.

37. In a telephone system, a repeater, circuits, an automatic switch for connecting the circuits with the repeater,y meansl for sending impulses first over one circuit and then over another, another automatic switch for extending the connection beyondsaid repeater, a circuit' in said other switch for controlling the operation thereof, means in said repeater for receiving said impulses and repeating them to said controlling circuit, and means in said repeater for holding said controlling circuit closed after the im- 38. In a telephone system, av repeater, circuits, an automatic switch for connecting the circuits with the repeater, means for sending impulses first over one circuit and then over another, another automatic switch for extending the connection beyond said repeater, a circuit in said other switch for controlling the operation thereof, means in said repeater for receiving said impulses and 'repeating them to said controlling circuit, and a bridge controlled' by said repeater for closing said controlling circuit.

39. Ina telephone system, a repeater, circuits, anw-automatic switch. for connecting 

